This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.
Mine roof bolts (under tension) have traditionally been solid round steel bars (smooth or rebar type) that are threaded to accommodate an expansion anchor or a delay mechanism nut with resin anchor. The tension tubular bolt eliminates the need for threads on the bolts which can cause problems such as: Bad threads; Poor torque (tension); Spinners on anchors; Spring-back; Threads sticking out of nuts in low seams. Various relevant patents are described as follows.
(I) Tadolini—U.S. Pat. No. 5,127,769 (written up in the “10th International Conference on Ground Control in Mining”—Title of Paper: Thrust Bolting—A New Innovation in Coal Mine Roof Support)
This teaching featured using a solid bar or bolt—anchored in resin—and pushed against the head of the bolt and plate; thus, the roof rock interface with the plate.
(II) Locotos—U.S. Pat. No. 5,387,060 Tubular Bolt
This tubular bolt is resin anchored, but does not feature a method to tension it.
(III) Mechanical Roof Bolts
Feature a solid bar, threaded to accept an expansion anchor (such as Frazer & Jones Co. F-2B).
This Bolt must be turned to expand the anchor and grab the hole. A certain small number of these bolts fail on installation due to a number of reasons, most of which are related to the external threads of the bolt or internal threads of the expansion anchor.
(IV) Tension Rebar Bolts
These bolts feature a threaded resin anchored solid rebar bolt. The threaded portion is on the bottom end of the bolt (resin anchor at top). A delay type nut is placed on the threaded end permitting the bolt to be spun through the resin to mix, and then held until resin hardens. After this, the delay nut is turned until the delay mechanism is overcome (i.e.: shear pin) and the bolt is tensioned with threads of the bolt emerging from the nut. These threads emerging from the nut can be a nuisance in low seams. A small portion of these bolts show extreme amounts of threads showing—indicating a possible incorrect installation.